Date: Mon, 15 Jul 2013 22:56:24 +0000 (UTC) From: Warren Block <wblock@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-projects@freebsd.org Subject: svn commit: r42288 - projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems Message-ID: <201307152256.r6FMuOZZ080787@svn.freebsd.org>
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Author: wblock Date: Mon Jul 15 22:56:23 2013 New Revision: 42288 URL: http://svnweb.freebsd.org/changeset/doc/42288 Log: Commit Allan Jude's modifications to the ZFS section so we can get to work on it. Submitted by: Allan Jude <allan.jude@gmail.com> Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml Modified: projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml ============================================================================== --- projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml Mon Jul 15 20:59:25 2013 (r42287) +++ projects/zfsupdate-201307/en_US.ISO8859-1/books/handbook/filesystems/chapter.xml Mon Jul 15 22:56:23 2013 (r42288) @@ -100,81 +100,635 @@ <title>The Z File System (ZFS)</title> <para>The Z file system, originally developed by &sun;, - is designed to use a pooled storage method in that space is only - used as it is needed for data storage. It is also designed for - maximum data integrity, supporting data snapshots, multiple - copies, and data checksums. It uses a software data replication - model, known as <acronym>RAID</acronym>-Z. - <acronym>RAID</acronym>-Z provides redundancy similar to - hardware <acronym>RAID</acronym>, but is designed to prevent - data write corruption and to overcome some of the limitations - of hardware <acronym>RAID</acronym>.</para> - - <sect2> - <title>ZFS Tuning</title> - - <para>Some of the features provided by <acronym>ZFS</acronym> - are RAM-intensive, so some tuning may be required to provide - maximum efficiency on systems with limited RAM.</para> - - <sect3> - <title>Memory</title> - - <para>At a bare minimum, the total system memory should be at - least one gigabyte. The amount of recommended RAM depends - upon the size of the pool and the ZFS features which are - used. A general rule of thumb is 1GB of RAM for every 1TB - of storage. If the deduplication feature is used, a general - rule of thumb is 5GB of RAM per TB of storage to be - deduplicated. While some users successfully use ZFS with - less RAM, it is possible that when the system is under heavy - load, it may panic due to memory exhaustion. Further tuning - may be required for systems with less than the recommended - RAM requirements.</para> - </sect3> - - <sect3> - <title>Kernel Configuration</title> - - <para>Due to the RAM limitations of the &i386; platform, users - using ZFS on the &i386; architecture should add the - following option to a custom kernel configuration file, - rebuild the kernel, and reboot:</para> - - <programlisting>options KVA_PAGES=512</programlisting> - - <para>This option expands the kernel address space, allowing - the <varname>vm.kvm_size</varname> tunable to be pushed - beyond the currently imposed limit of 1 GB, or the - limit of 2 GB for <acronym>PAE</acronym>. To find the - most suitable value for this option, divide the desired - address space in megabytes by four (4). In this example, it - is <literal>512</literal> for 2 GB.</para> - </sect3> - - <sect3> - <title>Loader Tunables</title> + is designed to future proof the file system by removing many of + the arbitrary limits imposed on previous file systems. ZFS + allows continuous growth of the pooled storage by adding + additional devices. ZFS allows you to create many file systems + (in addition to block devices) out of a single shared pool of + storage. Space is allocated as needed, so all remaining free + space is available to each file system in the pool. It is also + designed for maximum data integrity, supporting data snapshots, + multiple copies, and cryptographic checksums. It uses a + software data replication model, known as + <acronym>RAID</acronym>-Z. <acronym>RAID</acronym>-Z provides + redundancy similar to hardware <acronym>RAID</acronym>, but is + designed to prevent data write corruption and to overcome some + of the limitations of hardware <acronym>RAID</acronym>.</para> + + <sect2 id="filesystems-zfs-term"> + <title>ZFS Features and Terminology</title> + + <para>ZFS is a fundamentally different file system because it + is more than just a file system. ZFS combines the roles of + file system and volume manager, enabling additional storage + devices to be added to a live system and having the new space + available on all of the existing file systems in that pool + immediately. By combining the traditionally separate roles, + ZFS is able to overcome previous limitations that prevented + RAID groups being able to grow. Each top level device in a + zpool is called a vdev, which can be a simple disk or a RAID + transformation such as a mirror or RAID-Z array. ZFS file + systems (called datasets), each have access to the combined + free space of the entire pool. As blocks are allocated the + free space in the pool available to of each file system is + decreased. This approach avoids the common pitfall with + extensive partitioning where free space becomes fragmentated + across the partitions.</para> + + <informaltable pgwide="1"> + <tgroup cols="2"> + <tbody> + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-zpool"/>zpool</entry> + + <entry>A storage pool is the most basic building block + of ZFS. A pool is made up of one or more vdevs, the + underlying devices that store the data. A pool is + then used to create one or more file systems + (datasets) or block devices (volumes). These datasets + and volumes share the pool of remaining free space. + Each pool is uniquely identified by a name and a + <acronym>GUID</acronym>. The zpool also controls the + version number and therefore the features available + for use with ZFS. + <note><para>&os; 9.0 and 9.1 include + support for ZFS version 28. Future versions use ZFS + version 5000 with feature flags. This allows + greater cross-compatibility with other + implementations of ZFS. + </para></note></entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-vdev"/>vdev Types</entry> + + <entry>A zpool is made up of one or more vdevs, which + themselves can be a single disk or a group of disks, + in the case of a RAID transform. When multiple vdevs + are used, ZFS spreads data across the vdevs to + increase performance and maximize usable space. + <itemizedlist> + <listitem> + <para><anchor + id="filesystems-zfs-term-vdev-disk"/> + <emphasis>Disk</emphasis> - The most basic type + of vdev is a standard block device. This can be + an entire disk (such as + <devicename><replaceable>/dev/ada0</replaceable></devicename> + or + <devicename><replaceable>/dev/da0</replaceable></devicename>) + or a partition + (<devicename><replaceable>/dev/ada0p3</replaceable></devicename>). + Contrary to the Solaris documentation, on &os; + there is no performance penalty for using a + partition rather than an entire disk.</para> + </listitem> + + <listitem> + <para><anchor + id="filesystems-zfs-term-vdev-file"/> + <emphasis>File</emphasis> - In addition to + disks, ZFS pools can be backed by regular files, + this is especially useful for testing and + experimentation. Use the full path to the file + as the device path in the zpool create command. + All vdevs must be atleast 128 MB in + size.</para> + </listitem> + + <listitem> + <para><anchor + id="filesystems-zfs-term-vdev-mirror"/> + <emphasis>Mirror</emphasis> - When creating a + mirror, specify the <literal>mirror</literal> + keyword followed by the list of member devices + for the mirror. A mirror consists of two or + more devices, all data will be written to all + member devices. A mirror vdev will only hold as + much data as its smallest member. A mirror vdev + can withstand the failure of all but one of its + members without losing any data.</para> + + <note> + <para> + A regular single disk vdev can be + upgraded to a mirror vdev at any time using + the <command>zpool</command> <link + linkend="filesystems-zfs-zpool-attach">attach</link> + command.</para> + </note> + </listitem> + + <listitem> + <para><anchor + id="filesystems-zfs-term-vdev-raidz"/> + <emphasis><acronym>RAID</acronym>-Z</emphasis> - + ZFS implements RAID-Z, a variation on standard + RAID-5 that offers better distribution of parity + and eliminates the "RAID-5 write hole" in which + the data and parity information become + inconsistent after an unexpected restart. ZFS + supports 3 levels of RAID-Z which provide + varying levels of redundancy in exchange for + decreasing levels of usable storage. The types + are named RAID-Z1 through Z3 based on the number + of parity devinces in the array and the number + of disks that the pool can operate + without.</para> + + <para>In a RAID-Z1 configuration with 4 disks, + each 1 TB, usable storage will be 3 TB + and the pool will still be able to operate in + degraded mode with one faulted disk. If an + additional disk goes offline before the faulted + disk is replaced and resilvered, all data in the + pool can be lost.</para> + + <para>In a RAID-Z3 configuration with 8 disks of + 1 TB, the volume would provide 5TB of + usable space and still be able to operate with + three faulted disks. Sun recommends no more + than 9 disks in a single vdev. If the + configuration has more disks, it is recommended + to divide them into separate vdevs and the pool + data will be striped across them.</para> + + <para>A configuration of 2 RAID-Z2 vdevs + consisting of 8 disks each would create + something similar to a RAID 60 array. A RAID-Z + group's storage capacity is approximately the + size of the smallest disk, multiplied by the + number of non-parity disks. 4x 1 TB disks + in Z1 has an effective size of approximately + 3 TB, and a 8x 1 TB array in Z3 will + yeild 5 TB of usable space.</para> + </listitem> + + <listitem> + <para><anchor + id="filesystems-zfs-term-vdev-spare"/> + <emphasis>Spare</emphasis> - ZFS has a special + pseudo-vdev type for keeping track of available + hot spares. Note that installed hot spares are + not deployed automatically; they must manually + be configured to replace the failed device using + the zfs replace command.</para> + </listitem> + + <listitem> + <para><anchor + id="filesystems-zfs-term-vdev-log"/> + <emphasis>Log</emphasis> - ZFS Log Devices, also + known as ZFS Intent Log (<acronym>ZIL</acronym>) + move the intent log from the regular pool + devices to a dedicated device. The ZIL + accelerates synchronous transactions by using + storage devices (such as + <acronym>SSD</acronym>s) that are faster + compared to those used for the main pool. When + data is being written and the application + requests a guarantee that the data has been + safely stored, the data is written to the faster + ZIL storage, then later flushed out to the + regular disks, greatly reducing the latency of + synchronous writes. Log devices can be + mirrored, but RAID-Z is not supported. When + specifying multiple log devices writes will be + load balanced across all devices.</para> + </listitem> + + <listitem> + <para><anchor + id="filesystems-zfs-term-vdev-cache"/> + <emphasis>Cache</emphasis> - Adding a cache vdev + to a zpool will add the storage of the cache to + the L2ARC. Cache devices cannot be mirrored. + Since a cache device only stores additional + copies of existing data, there is no risk of + data loss.</para> + </listitem> + </itemizedlist></entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-arc"/>Adaptive Replacement + Cache (<acronym>ARC</acronym>)</entry> + + <entry>ZFS uses an Adaptive Replacement Cache + (<acronym>ARC</acronym>), rather than a more + traditional Least Recently Used + (<acronym>LRU</acronym>) cache. An + <acronym>LRU</acronym> cache is a simple list of items + in the cache sorted by when each object was most + recently used; new items are added to the top of the + list and once the cache is full items from the bottom + of the list are evicted to make room for more active + objects. An <acronym>ARC</acronym> consists of four + lists; the Most Recently Used (<acronym>MRU</acronym>) + and Most Frequently Used (<acronym>MFU</acronym>) + objects, plus a ghost list for each. These ghost + lists tracks recently evicted objects to provent them + being added back to the cache. This increases the + cache hit ratio by avoiding objects that have a + history of only being used occasionally. Another + advantage of using both an <acronym>MRU</acronym> and + <acronym>MFU</acronym> is that scanning an entire + filesystem would normally evict all data from an + <acronym>MRU</acronym> or <acronym>LRU</acronym> cache + in favor of this freshly accessed content. In the + case of <acronym>ZFS</acronym> since there is also an + <acronym>MFU</acronym> that only tracks the most + frequently used objects, the cache of the most + commonly accessed blocks remains.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-l2arc"/>L2ARC</entry> + + <entry>The <acronym>L2ARC</acronym> is the second level + of the <acronym>ZFS</acronym> caching system. The + primary <acronym>ARC</acronym> is stored in + <acronym>RAM</acronym>, however since the amount of + available <acronym>RAM</acronym> is often limited, + <acronym>ZFS</acronym> can also make use of <link + linkend="filesystems-zfs-term-vdev-cache">cache</link> + vdevs. Solid State Disks (<acronym>SSD</acronym>s) + are often used as these cache devices due to their + higher speed and lower latency compared to traditional + spinning disks. An L2ARC is entirely optional, but + having one will significantly increase read speeds for + files that are cached on the <acronym>SSD</acronym> + instead of having to be read from the regular spinning + disks. The L2ARC can also speed up <link + linkend="filesystems-zfs-term-deduplication">deduplication</link> + since a <acronym>DDT</acronym> that does not fit in + <acronym>RAM</acronym> but does fit in the + <acronym>L2ARC</acronym> will be much faster than if + the <acronym>DDT</acronym> had to be read from disk. + The rate at which data is added to the cache devices + is limited to prevent prematurely wearing out the + <acronym>SSD</acronym> with too many writes. Until + the cache is full (the first block has been evicted to + make room), writing to the <acronym>L2ARC</acronym> is + limited to the sum of the write limit and the boost + limit, then after that limited to the write limit. A + pair of sysctl values control these rate limits; + <literal>vfs.zfs.l2arc_write_max</literal> controls + how many bytes are written to the cache per second, + while <literal>vfs.zfs.l2arc_write_boost</literal> + adds to this limit during the "Turbo Warmup Phase" + (Write Boost).</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-cow"/>Copy-On-Write</entry> + + <entry>Unlike a traditional file system, when data is + overwritten on ZFS the new data is written to a + different block rather than overwriting the old data + in place. Only once this write is complete is the + metadata then updated to point to the new location of + the data. This means that in the event of a shorn + write (a system crash or power loss in the middle of + writing a file) the entire original contents of the + file are still available and the incomplete write is + discarded. This also means that ZFS does not require + a fsck after an unexpected shutdown.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-dataset"/>Dataset</entry> + + <entry></entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-volum"/>Volume</entry> + + <entry>In additional to regular file systems (datasets), + ZFS can also create volumes, which are block devices. + Volumes have many of the same features, including + copy-on-write, snapshots, clones and + checksumming.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-snapshot"/>Snapshot</entry> + + <entry>The <link + linkend="filesystems-zfs-term-cow">copy-on-write</link> + design of ZFS allows for nearly instantaneous + consistent snapshots with arbitrary names. After + taking a snapshot of a dataset (or a recursive + snapshot of a parent dataset that will include all + child datasets), new data is written to new blocks (as + described above), however the old blocks are not + reclaimed as free space. There are then two versions + of the file system, the snapshot (what the file system + looked like before) and the live file system; however + no additional space is used. As new data is written + to the live file system, new blocks are allocated to + store this data. The apparent size of the snapshot + will grow as the blocks are no longer used in the live + file system, but only in the snapshot. These + snapshots can be mounted (read only) to allow for the + recovery of previous versions of files. It is also + possible to <link + linkend="filesystems-zfs-zfs-snapshot">rollback</link> + a live file system to a specific snapshot, undoing any + changes that took place after the snapshot was taken. + Each block in the zpool has a reference counter which + indicates how many snapshots, clones, datasets or + volumes make use of that block. As files and + snapshots are deleted, the reference count is + decremented; once a block is no longer referenced, it + is reclaimed as free space. Snapshots can also be + marked with a <link + linkend="filesystems-zfs-zfs-snapshot">hold</link>, + once a snapshot is held, any attempt to destroy it + will return an EBUY error. Each snapshot can have + multiple holds, each with a unique name. The <link + linkend="filesystems-zfs-zfs-snapshot">release</link> + command removes the hold so the snapshot can then be + deleted. Snapshots can be taken on volumes, however + they can only be cloned or rolled back, not mounted + independently.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-clone"/>Clone</entry> + + <entry>Snapshots can also be cloned; a clone is a + writable version of a snapshot, allowing the file + system to be forked as a new dataset. As with a + snapshot, a clone initially consumes no additional + space, only as new data is written to a clone and new + blocks are allocated does the apparent size of the + clone grow. As blocks are overwritten in the cloned + file system or volume, the reference count on the + previous block is decremented. The snapshot upon + which a clone is based cannot be deleted because the + clone is dependeant upon it (the snapshot is the + parent, and the clone is the child). Clones can be + <literal>promoted</literal>, reversing this + dependeancy, making the clone the parent and the + previous parent the child. This operation requires no + additional space, however it will change the way the + used space is accounted.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-checksum"/>Checksum</entry> + + <entry>Every block that is allocated is also checksummed + (which algorithm is used is a per dataset property, + see: zfs set). ZFS transparently validates the + checksum of each block as it is read, allowing ZFS to + detect silent corruption. If the data that is read + does not match the expected checksum, ZFS will attempt + to recover the data from any available redundancy + (mirrors, RAID-Z). You can trigger the validation of + all checksums using the <link + linkend="filesystems-zfs-term-scrub">scrub</link> + command. The available checksum algorithms include: + <itemizedlist> + <listitem><para>fletcher2</para></listitem> + <listitem><para>fletcher4</para></listitem> + <listitem><para>sha256</para></listitem> + </itemizedlist> The fletcher algorithms are faster, + but sha256 is a strong cryptographic hash and has a + much lower chance of a collisions at the cost of some + performance. Checksums can be disabled but it is + inadvisable.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-compression"/>Compression</entry> + + <entry>Each dataset in ZFS has a compression property, + which defaults to off. This property can be set to + one of a number of compression algorithms, which will + cause all new data that is written to this dataset to + be compressed as it is written. In addition to the + reduction in disk usage, this can also increase read + and write throughput, as only the smaller compressed + version of the file needs to be read or + written.<note> + <para>LZ4 compression is only available after &os; + 9.2</para> + </note></entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-deduplication"/>Deduplication</entry> + + <entry>ZFS has the ability to detect duplicate blocks of + data as they are written (thanks to the checksumming + feature). If deduplication is enabled, instead of + writing the block a second time, the reference count + of the existing block will be increased, saving + storage space. In order to do this, ZFS keeps a + deduplication table (<acronym>DDT</acronym>) in + memory, containing the list of unique checksums, the + location of that block and a reference count. When + new data is written, the checksum is calculated and + compared to the list. If a match is found, the data + is considered to be a duplicate. When deduplication + is enabled, the checksum algorithm is changed to + <acronym>SHA256</acronym> to provide a secure + cryptographic hash. ZFS deduplication is tunable; if + dedup is on, then a matching checksum is assumed to + mean that the data is identical. If dedup is set to + verify, then the data in the two blocks will be + checked byte-for-byte to ensure it is actually + identical and if it is not, the hash collision will be + noted by ZFS and the two blocks will be stored + separately. Due to the nature of the + <acronym>DDT</acronym>, having to store the hash of + each unique block, it consumes a very large amount of + memory (a general rule of thumb is 5-6 GB of ram + per 1 TB of deduplicated data). In situations + where it is not practical to have enough + <acronym>RAM</acronym> to keep the entire DDT in + memory, performance will suffer greatly as the DDT + will need to be read from disk before each new block + is written. Deduplication can make use of the L2ARC + to store the DDT, providing a middle ground between + fast system memory and slower disks. It is advisable + to consider using ZFS compression instead, which often + provides nearly as much space savings without the + additional memory requirement.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-scrub"/>Scrub</entry> + + <entry>In place of a consistency check like fsck, ZFS + has the <literal>scrub</literal> command, which reads + all data blocks stored on the pool and verifies their + checksums them against the known good checksums stored + in the metadata. This periodic check of all the data + stored on the pool ensures the recovery of any + corrupted blocks before they are needed. A scrub is + not required after an unclean shutdown, but it is + recommended that you run a scrub at least once each + quarter. ZFS compares the checksum for each block as + it is read in the normal course of use, but a scrub + operation makes sure even infrequently used blocks are + checked for silent corruption.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-quota"/>Dataset + Quota</entry> + + <entry>ZFS provides very fast and accurate dataset, user + and group space accounting in addition to quotes and + space reservations. This gives the administrator fine + grained control over how space is allocated and allows + critical file systems to reserve space to ensure other + file systems do not take all of the free space. + <para>ZFS supports different types of quotas: the + dataset quota, the <link + linkend="filesystems-zfs-term-refquota">reference + quota (<acronym>refquota</acronym>)</link>, the + <link linkend="filesystems-zfs-term-userquota">user + quota</link>, and the <link + linkend="filesystems-zfs-term-groupquota"> + group quota</link>.</para> + + <para>Quotas limit the amount of space that a dataset + and all of its descendants (snapshots of the + dataset, child datasets and the snapshots of those + datasets) can consume.</para> + + <note> + <para>Quotas cannot be set on volumes, as the + <literal>volsize</literal> property acts as an + implicit quota.</para> + </note></entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-refquota"/>Reference + Quota</entry> + + <entry>A reference quota limits the amount of space a + dataset can consume by enforcing a hard limit on the + space used. However, this hard limit includes only + space that the dataset references and does not include + space used by descendants, such as file systems or + snapshots.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-userquota"/>User + Quota</entry> + + <entry>User quotas are useful to limit the amount of + space that can be used by the specified user.</entry> + </row> + + <row> + <entry valign="top"> + <anchor id="filesystems-zfs-term-groupquota"/>Group + Quota</entry> + + <entry>The group quota limits the amount of space that a + specified group can consume.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-reservation"/>Dataset + Reservation</entry> + + <entry>The <literal>reservation</literal> property makes + it possible to guaranteed a minimum amount of space + for the use of a specific dataset and its descendants. + This means that if a 10 GB reservation is set on + <filename>storage/home/bob</filename>, if another + dataset tries to use all of the free space, at least + 10 GB of space is reserved for this dataset. If + a snapshot is taken of + <filename>storage/home/bob</filename>, the space used + by that snapshot is counted against the reservation. + The <link + linkend="filesystems-zfs-term-refreservation">refreservation</link> + property works in a similar way, except it + <emphasis>excludes</emphasis> descendants, such as + snapshots. + <para>Reservations of any sort are useful + in many situations, such as planning and testing the + suitability of disk space allocation in a new + system, or ensuring that enough space is available + on file systems for audio logs or system recovery + procedures and files.</para></entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-refreservation"/>Reference + Reservation</entry> + + <entry>The <literal>refreservation</literal> property + makes it possible to guaranteed a minimum amount of + space for the use of a specific dataset + <emphasis>excluding</emphasis> its descendants. This + means that if a 10 GB reservation is set on + <filename>storage/home/bob</filename>, if another + dataset tries to use all of the free space, at least + 10 GB of space is reserved for this dataset. In + contrast to a regular <link + linkend="filesystems-zfs-term-reservation">reservation</link>, + space used by snapshots and decendant datasets is not + counted against the reservation. As an example, if a + snapshot was taken of + <filename>storage/home/bob</filename>, enough disk + space would have to exist outside of the + <literal>refreservation</literal> amount for the + operation to succeed because descendants of the main + data set are not counted by the + <literal>refreservation</literal> amount and so do not + encroach on the space set.</entry> + </row> + + <row> + <entry valign="top"><anchor + id="filesystems-zfs-term-resilver"/>Resilver</entry> + + <entry></entry> + </row> + + </tbody> + </tgroup> + </informaltable> + </sect2> - <para>The <devicename>kmem</devicename> address space can - be increased on all &os; architectures. On a test system - with one gigabyte of physical memory, success was achieved - with the following options added to - <filename>/boot/loader.conf</filename>, and the system - restarted:</para> + <sect2 id="filesystems-zfs-differences"> + <title>What Makes ZFS Different</title> - <programlisting>vm.kmem_size="330M" -vm.kmem_size_max="330M" -vfs.zfs.arc_max="40M" -vfs.zfs.vdev.cache.size="5M"</programlisting> - - <para>For a more detailed list of recommendations for - ZFS-related tuning, see <ulink - url="http://wiki.freebsd.org/ZFSTuningGuide"></ulink>.</para>; - </sect3> + <para></para> </sect2> - <sect2> - <title>Using <acronym>ZFS</acronym></title> + <sect2 id="filesystems-zfs-quickstart"> + <title><acronym>ZFS</acronym> Quick Start Guide</title> <para>There is a start up mechanism that allows &os; to mount <acronym>ZFS</acronym> pools during system @@ -189,8 +743,8 @@ vfs.zfs.vdev.cache.size="5M"</programlis <devicename><replaceable>da0</replaceable></devicename>, <devicename><replaceable>da1</replaceable></devicename>, and <devicename><replaceable>da2</replaceable></devicename>. - Users of <acronym>IDE</acronym> hardware should instead use - <devicename><replaceable>ad</replaceable></devicename> + Users of <acronym>SATA</acronym> hardware should instead use + <devicename><replaceable>ada</replaceable></devicename> device names.</para> <sect3> @@ -200,7 +754,7 @@ vfs.zfs.vdev.cache.size="5M"</programlis pool using a single disk device, use <command>zpool</command>:</para> - <screen>&prompt.root; <userinput>zpool create example /dev/da0</userinput></screen> + <screen>&prompt.root; <userinput>zpool create <replaceable>example</replaceable> <replaceable>/dev/da0</replaceable></userinput></screen> <para>To view the new pool, review the output of <command>df</command>:</para> @@ -324,7 +878,9 @@ example/data 17547008 0 175 <para>There is no way to prevent a disk from failing. One method of avoiding data loss due to a failed hard disk is to implement <acronym>RAID</acronym>. <acronym>ZFS</acronym> - supports this feature in its pool design.</para> + supports this feature in its pool design. RAID-Z pools + require 3 or more disks but yield more usable space than + mirrored pools.</para> <para>To create a <acronym>RAID</acronym>-Z pool, issue the following command and specify the disks to add to the @@ -333,7 +889,7 @@ example/data 17547008 0 175 <screen>&prompt.root; <userinput>zpool create storage raidz da0 da1 da2</userinput></screen> <note> - <para>&sun; recommends that the amount of devices used in + <para>&sun; recommends that the number of devices used in a <acronym>RAID</acronym>-Z configuration is between three and nine. For environments requiring a single pool consisting of 10 disks or more, consider breaking it up @@ -553,42 +1109,126 @@ errors: No known data errors</screen> <para>Refer to &man.zfs.8; and &man.zpool.8; for other <acronym>ZFS</acronym> options.</para> </sect3> + </sect2> - <sect3> - <title>ZFS Quotas</title> + <sect2 id="filesystems-zfs-zpool"> + <title><command>zpool</command> Administration</title> - <para>ZFS supports different types of quotas: the refquota, - the general quota, the user quota, and the group quota. - This section explains the basics of each type and includes - some usage instructions.</para> - - <para>Quotas limit the amount of space that a dataset and its - descendants can consume, and enforce a limit on the amount - of space used by filesystems and snapshots for the - descendants. Quotas are useful to limit the amount of space - a particular user can use.</para> + <para></para> - <note> - <para>Quotas cannot be set on volumes, as the - <literal>volsize</literal> property acts as an implicit - quota.</para> - </note> + <sect3 id="filesystems-zfs-zpool-create"> + <title>Creating & Destroying Storage Pools</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zpool-attach"> + <title>Adding & Removing Devices</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zpool-resilver"> + <title>Dealing with Failed Devices</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zpool-import"> + <title>Importing & Exporting Pools</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zpool-upgrade"> + <title>Upgrading a Storage Pool</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zpool-status"> + <title>Checking the Status of a Pool</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zpool-iostat"> + <title>Performance Monitoring</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zpool-split"> + <title>Splitting a Storage Pool</title> + + <para></para> + </sect3> + </sect2> + + <sect2 id="filesystems-zfs-zfs"> + <title><command>zfs</command> Administration</title> + + <para></para> + + <sect3 id="filesystems-zfs-zfs-create"> + <title>Creating & Destroying Datasets</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zfs-volume"> + <title>Creating & Destroying Volumes</title> + + <para></para> + </sect3> - <para>The - <literal>refquota=<replaceable>size</replaceable></literal> - limits the amount of space a dataset can consume by - enforcing a hard limit on the space used. However, this - hard limit does not include space used by descendants, such - as file systems or snapshots.</para> + <sect3 id="filesystems-zfs-zfs-rename"> + <title>Renaming a Dataset</title> - <para>To enforce a general quota of 10 GB for + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zfs-set"> + <title>Setting Dataset Properties</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zfs-snapshot"> + <title>Managing Snapshots</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zfs-clones"> + <title>Managing Clones</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zfs-send"> + <title>ZFS Replication</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zfs-quota"> + <title>Dataset, User and Group Quotes</title> + + <para>To enforce a dataset quota of 10 GB for <filename>storage/home/bob</filename>, use the following:</para> <screen>&prompt.root; <userinput>zfs set quota=10G storage/home/bob</userinput></screen> - <para>User quotas limit the amount of space that can be used - by the specified user. The general format is + <para>To enforce a reference quota of 10 GB for + <filename>storage/home/bob</filename>, use the + following:</para> + + <screen>&prompt.root; <userinput>zfs set refquota=10G storage/home/bob</userinput></screen> + + <para>The general + format is <literal>userquota@<replaceable>user</replaceable>=<replaceable>size</replaceable></literal>, and the user's name must be in one of the following formats:</para> @@ -622,8 +1262,8 @@ errors: No known data errors</screen> </listitem> </itemizedlist> - <para>For example, to enforce a quota of 50 GB for a user - named <replaceable>joe</replaceable>, use the + <para>For example, to enforce a user quota of 50 GB + for a user named <replaceable>joe</replaceable>, use the following:</para> <screen>&prompt.root; <userinput>zfs set userquota@joe=50G</userinput></screen> @@ -633,15 +1273,17 @@ errors: No known data errors</screen> <screen>&prompt.root; <userinput>zfs set userquota@joe=none</userinput></screen> - <para>User quota properties are not displayed by - <command>zfs get all</command>. - Non-<username>root</username> users can only see their own - quotas unless they have been granted the - <literal>userquota</literal> privilege. Users with this - privilege are able to view and set everyone's quota.</para> + <note> + <para>User quota properties are not displayed by + <command>zfs get all</command>. + Non-<username>root</username> users can only see their own + quotas unless they have been granted the + <literal>userquota</literal> privilege. Users with this + privilege are able to view and set everyone's + quota.</para> + </note> - <para>The group quota limits the amount of space that a - specified group can consume. The general format is + <para>The general format for setting a group quota is: <literal>groupquota@<replaceable>group</replaceable>=<replaceable>size</replaceable></literal>.</para> <para>To set the quota for the group @@ -678,35 +1320,10 @@ errors: No known data errors</screen> <screen>&prompt.root; <userinput>zfs get quota storage/home/bob</userinput></screen> </sect3> - <sect3> - <title>ZFS Reservations</title> + <sect3 id="filesystems-zfs-zfs-reservation"> + <title>Reservations</title> - <para>ZFS supports two types of space reservations. This - section explains the basics of each and includes some usage - instructions.</para> - - <para>The <literal>reservation</literal> property makes it - possible to reserve a minimum amount of space guaranteed - for a dataset and its descendants. This means that if a - 10 GB reservation is set on - <filename>storage/home/bob</filename>, if disk - space gets low, at least 10 GB of space is reserved - for this dataset. The <literal>refreservation</literal> - property sets or indicates the minimum amount of space - guaranteed to a dataset excluding descendants, such as - snapshots. As an example, if a snapshot was taken of - <filename>storage/home/bob</filename>, enough disk space - would have to exist outside of the - <literal>refreservation</literal> amount for the operation - to succeed because descendants of the main data set are - not counted by the <literal>refreservation</literal> - amount and so do not encroach on the space set.</para> - - <para>Reservations of any sort are useful in many situations, - such as planning and testing the suitability of disk space - allocation in a new system, or ensuring that enough space is - available on file systems for system recovery procedures and - files.</para> + <para></para> <para>The general format of the <literal>reservation</literal> property is @@ -733,6 +1350,141 @@ errors: No known data errors</screen> <screen>&prompt.root; <userinput>zfs get reservation storage/home/bob</userinput> &prompt.root; <userinput>zfs get refreservation storage/home/bob</userinput></screen> </sect3> + + <sect3 id="filesystems-zfs-zfs-compression"> + <title>Compression</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zfs-deduplication"> + <title>Deduplication</title> + + <para></para> + </sect3> + + <sect3 id="filesystems-zfs-zfs-allow"> + <title>Delegated Administration</title> + + <para></para> + </sect3> *** DIFF OUTPUT TRUNCATED AT 1000 LINES ***
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